1. Field of the Invention
The present invention relates to a return mechanism of an actuating drive.
2. State of the Art
The function of a return mechanism of an actuating drive for valves is to transmit a motion of the servo piston to a return sleeve in a control block. When hydraulic pressure acting on the servo piston rises or drops, the servo piston executes a stroke motion in one direction, the length of which is information variable for the transmission mechanism acting on the return sleeve in the control block inasmuch as the displacement of the return sleeve always triggers a hydraulic feedback which restores the equilibrium in the servo piston.
It is known to transmit stroke motion of a servo piston to a return sleeve in a control block by a series of linkages, connecting links and eccentric disks.
The disadvantages of known embodiments are that, inaccuracies cannot be prevented from occurring in the transmission of the stroke motion of the servo piston to the return sleeve, whether on account of kinematic friction losses or because of bearing play in the linkages or because of the inherent risk of jamming of the transmission mechanism itself. It can therefore be said that the designs provided in the prior art are unable to provide a satisfactory solutions to the problem of transmitting stroke motion of the servo piston to the return sleeve--without time-lag, without mechanical fault and without inaccuracies in stroke lengths. All of these shortcomings can cause errors which can have an effect on controllability.